Elastic strand construction

ABSTRACT

An elastic strand construction comprising a plurality of spaced ribs separated by thin zones is provided. The elastic strand construction is preferred for applications in disposable garments or the like. A method of manufacturing the preferred elastic strand comprises extrusion of polymeric material through a profiled die or the like. In the alternative, a method of formation comprising extrusion between a profiled roller arrangement is described. A preferred disposable garment construction utilizing elastic strands according to the present invention is described.

This is a continuation of application Ser. No. 07/464,620 filed Jan. 3,1990 now abandoned, which is a continuation of application Ser. No.07/137,258 filed Dec. 23, 1987, now abandoned.

FIELD OF THE INVENTION

The present invention relates to the construction of elastic membersutilizable in disposable diapers or similar articles. More particularly,the present invention relates to elongate elastic members formable fromextrusion processes or the like, and having preferred, advantageous,physical characteristics.

BACKGROUND OF THE INVENTION

Elastic or stretchable strands have found considerable use, especiallyin the disposable garment industry. The term "disposable garment" ismeant to refer to articles intended to be worn only once or temporarily,with ultimate disposal rather than laundering. Examples include:diapers; adult incontinence garments; hospital garments such as surgicalgowns, caps or shoe covers; disposable pajamas; laboratory coats; showercaps and similar items. Generally, such garments are made of lightweightfilm or sheet material such as: thermoplastic materials; non-wovencoated films or papers; or, composites of one or more of these types ofmaterials. Since low cost manufacture is generally a criticalrequirement, such garments are often manufactured using techniques suchas die-cutting, adhesive-bonding, heat-sealing and sonic-sealing; ratherthan through application of stitching or sewing methods utilized in moreexpensive, longer-lasting, textile garments.

It has been found desirable in such garments to provide elasticconstructions in the vicinity of openings, such as to accommodate awearer's arm, neck, waist, head or leg. Elasticity in these portions ofthe garment accomplishes numerous functions including: insuring snug fitfor a variety of sizes of users; and, in instances such as disposablebaby diapers, providing for a sealing or containing construction, forexample around a baby's legs, to prevent or reduce leakage.

Two primary, related, forms of providing for elasticized openings havebeen developed. In a first of these an elastic member is stretched andis attached to the article in an elastically contractible condition.After attachment to the article, tension is released and the elasticstrand contracts, bunching up or shirring the article. A strand, forexample, so attached around a leg opening will cause the leg opening tocontract. If the contracted leg opening is smaller in diameter than aleg projecting therethrough during use, in such use the elastic memberwill be stretched open somewhat, and will press snugly against the legmember, generating a snug fit or closing relationship.

A variety of methods of attachment of the elastic member to the garmentor substrate have been developed. These include heat-sealing, sonicwelding and pressure-sensitive adhesives or the like. In some instancesspaced adhesive units have been utilized to advantage, in providing forrelative strength or preferred shirring patterns.

A variety of elastic strand constructions, for utilization as describedabove, have been developed. Included in these are single strandarrangements. A problem with such arrangements is that they arerelatively susceptible to problems with failure, unless made relativelystrong. A reason for this is that the failure of a single point ofattachment or adhesion can cause a complete product failure. Further,should the single elastic member fracture or break, substantiallycomplete failure may also result.

Another problem with a single strand arrangement is that only arelatively narrow seal or closure is formed; and, if made relativelytight, irritation to the wearer's skin in a very narrow, localized,region or band may result.

As a result of the above problems, a variety of alternates to a singlenarrow band arrangement have been developed. For example, a plurality ofindividual, spaced, bands have been utilized to provide a rather wideelastic area. Also, net arrangements, i.e. cross-connected bands, havebeen developed. In some instances relatively wide elastic tapearrangements have been proposed. Also, a wide band comprising aplurality of elongate members fused, longitudinally, to one another hasalso been developed.

While the above-described arrangements have their uses and advantages,none is completely satisfactory. In multiple strand arrangements or netarrangements, attachment to the substrate or garment may pose a problem.A reason for this is that only a relatively narrow point for adhesiveattachment is provided, i.e., a point of engagement between a relativelynarrow strand member and the wider substrate. A narrow point of adhesionposes a substantial risk of failure, and thus is a problem. Further,multiple strand arrangements can be relatively expensive to construct,as complicated and precise attachment mechanisms and adhesiveapplication arrangements may be required.

Net arrangements may have advantages but can still pose problems, due inpart to cost of formation. Also, if thin or narrow strips are used,attachment may still be difficult.

Wide, thick, elastic strips are also not completely satisfactory. Insome instances, they may be so thick and strong not to stretchsufficiently for comfort. In other instances, they may be relativelyexpensive to produce, since a relatively large amount of material may beused in their construction.

A second major method of providing for an elastic strand member on asubstrate such as a disposable garment or the like, is throughutilization of a strand of heat shrinkable elastic material. Generally,the material is affixed to the substrate in a dimensionally heatunstable state. The substrate and elastic member combination is thenexposed to activating heat, to shrink the elastic component and generategathering or shirring. If properly chosen, the material used for theelastic strand can be provided such that once shrunk it will beappropriately elastic, and thus will stretch around an arm, leg, neck,etc. to provide the desired closing or sealing relationship.

The heat-shrink approach has been utilized in a variety of physicalembodiments. For example, multiple strand arrangements may be utilized,as well as net arrangements and the like. In at least one application,multiple strands have been provided within a composite substratearrangement.

The problems with conventional heat shrinkable elastic strandarrangements have generally been parallel to those described above. Ifmultiple strand arrangements are utilized, they may be relativelycomplicated to construct or apply. Composite structural relationshipsmay be too expensive for use in many types of disposable items. Problemswith placement of adhesive may result, if relatively narrow strands areused. If relatively wide strands are used, there may be problems withinsufficient elasticity and/or excessive cost of materials.

It is important to note again that a primary use of elastic strands suchas those of concern is to provide for shirring of substrates indisposable garments. It is significant, therefore, to maintain costs ator near a substantial minimum in order to obtain a competitiveadvantage. Thus, relatively complicated composite arrangements,relatively complicated multi-strand attachment mechanism and relativelydifficult to utilize adhesive arrangements are generally to be avoided,if possible. Further, it is preferred to utilize a minimum amount ofelastic strand material per substrate or garment, in order to maintainlow construction costs. It is important to provide an elasticconstruction which will be efficient and effective, in order toaccommodate the demands of the marketplace and competition.

What has been needed has been an elastic strand construction which isrelatively easy to achieve and to mount on or in association withsubstrates such as disposable garments or the like. Further, what hasbeen needed has been such a strand construction which is efficient andeffective in use, to provide for a good, comfortable closing or sealingarrangement when utilized around an arm or leg aperture, or the like.Finally, there has been a need for such an elastic strand which can bemanufactured in large quantities relatively quickly, efficiently, andinexpensively.

SUMMARY OF THE INVENTION

The present invention concerns: a preferred elastic strand construction;a method of forming elastic strands of the preferred construction;preferred methods of use of elastic strands constructed according to thepresent invention; and, disposable garment constructions utilizingelastic strands of the preferred construction.

Elastic strands arrangements according to the present inventioncomprise: an elastic strand having a plurality of laterally spacedlongitudinal ribs, each of which has at least a first thickness.

A preferred method of manufacturing an elastic strand according to theinvention includes the steps of: providing a die having an orificeshaped to define a plurality of thick zones, each of which is separatedby a thin zone, in material extruded therethrough; providing a hotextrudable thermoplastic elastomer; extruding the hot thermoplasticelastomer through the profiled die to form a hot ribbon of extrudedelastomer having: a plurality of laterally spaced longitudinal ribs,each of which has at least a first thickness; and, a substantiallycontinuous longitudinal transition zone extending between and attachedto each of the longitudinal ribs, each transition zone having athickness less than the first thickness and substantially equal to theprofiled die thin zone; and, quenching the hot ribbon.

An alternate method of manufacturing an elastic strand according to thepresent invention includes the steps of: providing a hot extrudablethermoplastic elastomer; providing an extrusion system for generating ahot elongate ribbon of the thermoplastic elastomer; providing a rollersystem including first and second rollers having a nip therebetween; thefirst roller having a profiled outer surface including a plurality ofspaced substantially parallel grooves therein; extruding the elastomerthrough the extrusion system to form a hot elongate ribbon; directingthe hot elongate ribbon through the nip in the roller system, whereinthe first roller outer surface forms a plurality of elongate parallellongitudinal ribs in the ribbon; and cooling the ribbon after formationof the ribs therein.

A proposed method of manufacturing thermally unstable, heat shrinkablestrands according to the present invention includes the step of lengthorienting the strands subsequent to formation by one of the methodsdescribed above. Length orientation involves stretching the strand atsomewhat elevated temperatures and allowing the strand to cool whileheld in the stretched state. Process conditions, i.e. temperature, nippressure, length differential, will be dictated by the desired amount ofstretch and the chemical composition of the strands, and are easilyselected by those skilled in the art.

A preferred article, such as a disposable diaper, according to thepresent invention comprises: a substrate; and, an elastic strand mountedon the substrate, the elastic strand having: a plurality of laterallyspaced ribs, each of the ribs having at least a first thickness; and, asubstantially continuous longitudinal transition zone extending betweenand attached to each longitudinal rib, each transition zone having athickness less than the first thickness.

In general, elastic strands according to the invention compriselongitudinally contoured or ribbed unitary strips. That is, each strandhas spaced thicker zones or ribs preferably running lengthwise, andsubstantially no apertures or net construction. Substantially continuoustransition or thinner zones run substantially completely along andbetween the elongate thicker zones or ribs, spacing each rib from thenext adjacent rib. The thicker ribs, as a result of the separation, inpart constitute individual regions of contraction force. The thinnerzone(s) constitute a means of combining the partially independentthicker elastic zones or ribs into a unitary construction, for ease ofmanufacture, application and use. While all embodiments of the presentinvention include a plurality of spaced ribs, it is noted that at leastone embodiment (that of only 2 ribs) may include only one thinner ortransition zone.

Certain preferred elastic strands according to the present inventionhave one substantially flat, i.e. non-ribbed, side to facilitatemounting to the substrate. That is, for this embodiment the strand hasopposite surfaces, one of which is flat, the other having the ribsthereon and projecting outwardly therefrom. The relatively flat sidefacilitates mounting since it provides an overall relatively broadsurface for engagement with adhesives or for heat-sealing,sonic-welding, etc. As a result, failure of adhesion at any particularlocal point is not likely to substantially inhibit overall operabilityof the elastic strand in providing the shirred construction. Further,attachment to a substrate is relatively simple, since only onerelatively wide strand is used, with problems of handling multiple,narrow, strands avoided.

Preferred elastic strands according to the present invention are madefrom extrudable thermoplastic elastomeric materials. According to onepreferred method of manufacture, the desired strand construction isformed by extruding of hot thermoplastic material through anappropriately profiled die. Such an extrusion process is generallyfollowed by immediate quenching, in a water bath or the like, tofacilitate retention of the desired physical shape.

According to an alternate method of forming elastic strands profiledaccording to the present invention, an elongate extruded strip ofrelatively hot moldable thermoplastic material is directed through a nipbetween adjacent rollers of a roller mechanism. At least one of therollers is provided with a profiled surface of appropriate design togenerate shaping of the hot strip into a desired form. Preferably, atleast one of the rollers is a chilled roller or cold roller,facilitating cooling of the elastic strand sufficiently so that themolded strand will retain its shape.

Preferred methods of use of elastic strands according to the presentinvention involve attachment to a substrate to be shirred, by means ofadhesives, sonic-welding, heat-sealing or similar techniques. Ifnon-heat shrinkable elastomeric strands are formed, generally the methodof use involves stretching the elastic strand material a desired amount,before attaching it to the substrate. For this method, attachment occurswhile the elastic strand is under tension, so that once attached andwhen tension is released, a bunching, gathering or shirring of thesubstrate occurs. If heat shrinkable strands are formed, as describedsupra, they may be attached without substantial tension, and thenheat-treated to shrink and cause shirring.

The present invention also concerns an overall substrate or garmentarrangement having an elastomeric portion formed from attachment of anelastic strand as described above, to a selected portion of thesubstrate.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention while illustratingfeatures thereof. It will be understood that in some instances relativematerial thicknesses, and relative component sizes, may be shownexaggerated for clarity. It will also be understood that some of thedrawings are schematic only and thus are representative of a variety ofmethods or constructions that may be utilized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary top perspective view of an elastic strandarrangement according to the present invention.

FIG. 2 is a fragmentary bottom perspective view of the arrangement shownin FIG. 1.

FIG. 3 is a cross-sectional view taken generally along line 3--3, FIG.1.

FIG. 4 is a cross-sectional view of an alternate embodiment of thepresent invention.

FIG. 5 is a cross-sectional view of a second alternate embodiment of thepresent invention.

FIG. 6 is a cross-sectional view of a third alternate embodimentaccording to the present invention.

FIG. 7 is a fragmentary perspective view of a profile die arrangementutilizable for creation of an elastic strand according to FIG. 1.

FIG. 8 is a schematic elevational view of a method of forming an elasticstrand arrangement according to the present invention.

FIG. 9 is an elevational schematic view of an alternate method offorming an elastic strand arrangement according to the presentinvention.

FIG. 10 is a cross-sectional view taken generally along line 10--10,FIG. 9.

FIG. 11 is a fragmentary cross-sectional view taken generally along line11--11, FIG. 4.

FIG. 12 is a perspective view of a disposable diaper incorporating anelastic strand arrangement according to the present invention, withportions broken away to show internal detail.

DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATE EMBODIMENTS

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but rather as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed system or structure.

THE ELASTIC STRAND CONSTRUCTION

FIGS. 1-3 illustrate a preferred elastic strand arrangement according tothe present invention. Referring to FIG. 1, the reference numeral 1generally designates the preferred strand construction. Strand 1comprises an elongate strip 2 having first and second opposite surfacesor surface portions 3 and 4 respectively. Strip 2 is continuous andunitary in construction; that is, it is formed in one piece andpreferably does not contain any pattern of apertures or holes therein.As a result of this construction, attachment of strip 2 to a substrate,such as a disposable garment or diaper, is facilitated. A reason forthis is that relatively large areas of strand are available as bondingsites. For the embodiment shown in FIGS. 1-3, surface 4 provides abonding surface for attachment to a garment or the like. For thepreferred embodiment depicted, surface 4 is substantially flat, FIG. 2,thus facilitating the attachment process.

Unitary strip 2 includes thereon a plurality of spaced ribs, or thickzones, 10. The ribs 10 preferably extend substantially parallel to oneanother along the entire length of strip 2. The ribs 10 are spaced fromone another by substantially continuous thin zones or areas 11.Preferably strip 2 is formed from an elastomeric substance in such away, for example as described below, that the composition of strip 2 isconstant throughout. That is, the thin zones or areas 11, and the thickzones or ribs 10, are formed of the same material. For the preferredembodiment, ribs 10 are formed in, and protrude outwardly from, surface3.

The purposes of the thick zones 10 and thin zones 11 differ somewhat,and advantages are obtained from the presence of both. The thick zones10 provide, to a great extent, for much of the longitudinal strength andelasticity of strip 2. That is, the ribs 10, being thick and of anelastomeric substance, provide for significant retractive tensile force.

The relatively thin zones 11 provide unique advantages. First, theyfacilitate attachment of multiple ribs 10 to the substrate, since thezones 11 maintain the ribs 10 in proper position with respect to oneanother and permit all ribs 10 to be readily handled by a singleapplicator or application device, simultaneously. Further, in thepreferred embodiment, the thin zones 11 provide a broad surface forattachment of adhesives or the like, to facilitate attachment to almostany substrate.

An overall spaced relationship between the ribs 10, maintained by thinzones 11, is preferred for numerous reasons. First, a relatively broadelastic band width is provided. A broad elastic band both isaesthetically pleasing and more comfortable. Also, a better seal orenclosure results, since a greater surface area is involved. Failure ofa single rib 10 is unlikely to substantially detract from elasticity ofthe overall arrangement since other ribs are present and the thin zones11 will help disperse tension. Further, any crimp which may form in aportion of strip 2, or any sharp object brought in associationtherewith, will be unlikely to substantially adversely affect all ribs10 at the same time. Thus, the structural integrity of strip 2 is moreeasily maintained during application, use and under stress conditions.

For the embodiments shown in FIGS. 1-3, the strip 2 is depicted withthree ribs 10. It will be understood, however, that a plurality ofalternate embodiments may be provided, having various numbers oflongitudinal ribs 10, and thin zones 11. Included in the possibilitiesis an embodiment, not shown, including two ribs separated by a singlethin zone.

In FIG. 3 a cross-section of strip 2 is depicted. From FIG. 3, it willbe understood that the zones 11 are very thin, relative to the ribs 10.While a variety of ratios of rib thickness to thin zone thickness may beutilized in arrangements according to the present invention, generallyratios between about 2/1 and about 10/1 will be preferred. Such ratioslead to acceptable overall integrity, while at the same time retainingmuch of the longitudinal strength, and elasticity of the overallarrangement, in the rib portions of the strip 2.

It will be understood that the overall thickness of the strip 2, andparticularly the ribs 10 thereof, will depend in part upon the nature ofthe elastomeric material from which the strip 2 is formed, and also theoverall strength of strip 2 intended. For preferred applications, suchas strips for disposable diapers or the like, the overall thickness ofthe ribs 10 will generally be in the range of 0.100 millimeters (mm) to0.635 mm, and preferably about 0.150 mm to 0.635 mm.

The overall width of the thick zones, and thin zones, is generallydictated by the overall strength of the strip desired, and the width ofelastic band desired for a particular application. For most applicationsinvolving unitary strips 2 for attachment to disposable diapers or thelike, the range of widths for the thicker zones will generally be about0.250 mm to 5.1 mm, and preferably about 0.760 mm to 2.5 mm, and theoverall width of the thinner zones 11 will be in the range of about0.250 mm to 5.10 mm, preferably 0.760 mm to 2.50 mm.

Preferably the thin zones 11 are relatively wide, by comparison to thewidth of the ribs 10, to insure that the ribs 10 are well spaced apart.One reason for this is that in many applications it is desired to insurethat the ribs 10 can, at least in part, act independently of one anotheras stretching elements. Thus, again, failure of one is unlikely toaffect the others. Another reason for broad spacing is to avoid injuryto adjacent ribs, if one rib is brought under stress from crimping orcontact with a sharp object or the like. Another reason for relativelywide spacing is to generate a relatively wide elastic band, to reduceskin irritation. Preferably, the width of the average thinner zone 11 isat least 50 percent of the width of the average rib 10. It will beunderstood that the thin zones 11 need not all have the same width.

From FIG. 2, an advantage to the preferred embodiment having therelatively flat lower surface 4 is apparent. Since surface 4 isrelatively broad, and flat, adhesive can be readily applied betweensurface 4 of strip 2 and a portion of a substrate such as a disposablediaper or the like.

It is noted that the ribs 10 of the embodiment of FIGS. 1-3 have agenerally rounded outer surface, corresponding to a semi-oval, orsemi-circular arrangement. It will be understood that a variety ofshapes may be utilized. For example, in FIG. 4, a cross-section of anembodiment is illustrated wherein the ribs 20 have a generally squarecross-section and are separated by transition zones 21. In FIG. 5, anoverall oval cross-section for ribs 22 is shown. From comparison ofFIGS. 3, 4 and 5 it will be understood that a variety of cross-sectionalshapes can be provided. Each of the types of cross-sections shown mayhave advantages for particular applications, especially relating togeneral overall aesthetics, strength, stretch and ease of manufacture.

It is noted that each of the embodiments of FIGS. 3, 4 and 5 has asurface, corresponding to lower surface 4, FIG. 3, which is relativelybroad and flat. While advantages can be obtained from such anarrangement, such a flat surface is not required to obtain some of theadvantages of the present invention, as is illustrated by the embodimentof FIG. 6.

In FIG. 6, an overall unitary strip 24 having a plurality of ribs 25attached to one another by means of elongate thin zones 26 is shown. Theembodiment of FIG. 6 differs significantly from that of the previousfigures, in that the ribs 25 project in both directions (here shown asup and down) from thin zones 26; that is, opposite surfaces 28 and 29both have ribs therein. Such an arrangement may be preferred, in somesituations, for aesthetics. Also, such an arrangement may lead to a moreconsistent stretch of each rib 26, along its cross-section, duringstress, for example during application to a substrate. That is, upperand lower surfaces 28 and 29 may be stressed substantially the sameduring stretching and application. Such would not as readily be thecase, for example, for the embodiment in FIG. 5 since lower portions ofthe ribs 20 are in a different spatial relationship with respect to thetransition zones 21, than are upper portions of the ribs 20.

It is noted that the embodiment of FIG. 6 may, in some applications, besomewhat more difficult to mount than the previously describedembodiment, since no extremely broad flat surface is provided tofacilitate mounting. Nevertheless, especially if a strip according toFIG. 6 were manufactured of sufficiently soft material, it could besqueezed flat enough to facilitate mounting. Further, if at least someribs having a sufficiently wide cross-section are chosen, mounting willbe facilitated. This is exemplified in FIG. 6, by the particularly widecentral rib 31. It will be understood that although for the embodimentshown in FIG. 6 the opposite surfaces 28 and 29 are substantiallyidentical, there is no requirement that they be so. That is, the ribs ofdifferent surfaces may have different profiles, and indeed need notnecessarily be located opposite one another.

For the embodiments shown in FIGS. 3 and 4, all ribs had a substantiallyidentical cross-section. It will be understood by comparison to FIGS. 5and 6, that such is not required in all embodiments. Ribs havingdifferent areas of cross-section, and indeed different overall shapes,may be utilized to advantage in a number of ways. For example, differentrib thicknesses, i.e., sizes and strengths, may provide for increasedstrength and resistance to stretching over one selected portion of theoverall strip width. This may be useful, for example, in providing asnug fit in a portion of a garment or the like sized for fitting over amember not of constant cross-sectional area. For example, a typicalperson's wrist grows larger in circumference as the elbow is approached.If a wide elastic member according to the present invention is to beutilized in a cuff of a garment, it may be desired to have a portioncloser to the elbow be less resistant to stretch, than a portion closeto the hand, in order to facilitate comfort. This could be readilyaccomplished through the utilization of ribs which are relatively thin,nearer the elbow, by comparison to those ribs nearer the hand.

Another reason why a variety of shapes or designs of ribs may bedesired, is for aesthetics. While items according to the presentinvention are generally intended to be disposable, attractive designsmay often still be desired, and may be achievable in strips according tothe present invention.

METHOD OF FORMATION

A particular advantage to elastic strand constructions according to thepresent invention is that they may be rapidly, efficiently, convenientlyand relatively inexpensively manufactured. A reason for this is that theoverall unitary construction lends itself toward manufacture fromextrusion techniques. Since no netting, or aperture, arrangement isinvolved, the manufacturing process is facilitated. Two particularlyconvenient methods of manufacture are depicted in FIGS. 7-11. The methodof FIGS. 7 and 8 concerns formation by extrusion through a profiled die.The method of FIGS. 9-11 concerns formation by extrusion through a nipbetween rollers.

A. FORMATION BY EXTRUSION THROUGH A PROFILE DIE

Generally, the material from which unitary strands according to thepresent invention are formed is such that when it is hot it issubstantially pliable and/or formable, but once cooled it retains aselected configuration. As previously explained, the unitary strandsaccording to the invention may be of either of two types, a first typewhich is formed into a construction for application to a substrate in astretched state; and a second type which is formed thermally unstable,so that when heated it will shrink considerably to shirr a substrate towhich it is attached. Either of these forms may be manufactured byeither of the methods described herein.

Since the raw material for formation of the unitary strands according tothe present invention is extrudable when hot, a particularly efficientmethod of manufacture involves extrusion through a profile die, i.e. adie of appropriate configuration for shaping hot material extrudedtherethrough. Referring to FIG. 7, die 43 is depicted having a profiledchannel 44 of appropriate shape to form a unitary strand according tothe present invention. It will be understood that profiled channel 44may have a variety of shapes, to accommodate unitary strands ofdifferent configurations. The channel 44 of die 43 depicted is of ashape appropriate to form the strand of FIG. 4. Die 43 is shown as beingsuch that channel 44 may be removed and replaced by a channel ofdifferent shape, if desired.

Generally strands of the present invention are produced by: extrudingthe hot polymer or polymer blend, typically at a temperature of about150° C. to 235° C., through a profiled extrusion die such as die 43;and, quenching, typically upon passing the formed strand through awater-filled quench tank with a submerged take-away. This process isrepresented, schematically, in FIG. 8.

Referring to FIG. 8, profiled die 50 is depicted with a line or ribbon51 of hot extruded material extending therefrom, into quench tank 52.Tank 52 is filled with water 53, which water may be cooled in someinstances, to for example 4°-16° C. Upon quenching the ribbon 51 iscooled sufficiently to retain its shape. Idler rollers 56 are showndirecting the quenched ribbon 57 to a storage roller 58.

The example represented in FIG. 8 utilizes a profiled die that has theapproximate shape of the final strands. In preferred applications theratio of the land length to the opening height of the profiled die is atleast 10. This ratio is the length of the flow path through the die, tothe thickness of the opening. While other ratios may be utilized, inpreferred applications, such a ratio will be used as it leads to readyformation of desired strands. In FIG. 8, reservoir and extruder 59 isshown forcing material through die 50.

Desired extruded shapes can be made from profile dies cut other thanwith the desired final shape; for example by varying land length tochange the flow pattern through the die plate in order to cause more (orless) material to flow through specific regions. Such dies are lessflexible with respect to varying materials and run conditions, andtherefore are not preferred.

B. SHAPING THROUGH UTILIZATION OF A PROFILED ROLLER ARRANGEMENT

FIGS. 9-11 depict an alternate method of construction of unitary strandsaccording to the present invention. Generally, the method involvesextrusion between rollers appropriately profiled to cause a preferredconfirmation in the strand. The overall method is depicted schematicallyin FIG. 9.

Referring to FIG. 9, an extruder in combination with a slot extrusiondie 65 is shown with a ribbon 66 of hot moldable extrudate projectingoutwardly therefrom. The ribbon 66 is passed through a nip 67 betweenrollers 70 and 71. Reference numeral 72 designates a reservoir andextruder of polymer material.

Preferably at least one of the rollers 70 and 71 is chilled, that is itis cooled sufficiently so that it will cause product ribbon 73 to retainthe desired profile or configuration.

Rollers 70 and 71 form an overall roller mechanism 75 profiled in amanner causing a preferred shaping of hot ribbon 66 as it passestherethrough. For example, roller 70 may include slots, grooves or thelike therein, which generate a preferred shape of ribbon 73. Referringto FIGS. 10 and 11, an example is given. In FIG. 10 a side elevationalview of ribbon 66 is presented. It will be understood that die 65provides ribbon 66 with a generally rectangular, i.e. non-profiled,cross-section.

In FIG. 11, formed ribbon 73 is shown passing outwardly from betweenrollers 70 and 71. The rollers 70 and 71 are profiled appropriately togive ribbon 73 a selected shape. In particular, roller 70 is shownprofiled at section 76, by means of recessed parallel grooves, to giveribbon 73 a cross-sectional shape analogous to strand 2, FIG. 1. It willbe understood that a variety of selected shapes may be similarly formed.Preferably, the method is utilized to provide strands having the desiredelongate longitudinal ribs separated by thin zones.

Preferred chilling temperatures for the chilled rollers(s) willprimarily depend upon the elastomer composition, melt viscosity andcontact time.

USE OF THE ELASTIC STRANDS IN ARTICLES

It will be readily understood that the unitary elastic strands of theinvention may be utilized in a variety of articles and in a variety ofmanners. It is anticipated that a preferred use will involveapplications to disposable diapers, incontinence garments or the like,particularly around leg apertures. Such an application is illustrated inFIG. 12. Referring to FIG. 12, a disposable diaper arrangement 85 isdepicted. It will be understood that the arrangement 85 may be of avariety of designs shapes or configurations. Generally, diaper 85comprises a substrate 86, to be provided with elastic bands.Specifically, attached to the substrate 86 are strips 87 of unitarystrand material according to the present invention. The strips 87 may bemounted, if desired, between layers of an overall composite constructionfor substrate 86. For the embodiment shown in FIG. 12, strips 87 arerepresented by phantom lines, to indicate that indeed they are out ofview, underneath protective layers.

Application of strips 87 to substrate 86 may be accomplished by avariety of means, including efficient mechanical means involvingapplication of the strips 87 from a feed roller with utilization ofvarious cutting and adhesive mechanisms; or, through utilization ofvarious sonic-welding or heat sealing methods. As has previously beenexplained, in some instances strip 87 may be formed such that it isapplied in a thermally stable, but stretched state, with shirringautomatically caused once the tension is released. In the alternative,strips 87 may be thermally unstable, heat-shrinkable material asdescribed supra, applied in an untensioned state, and then treated withheat to shrink and cause appropriate shirring.

ELASTIC STRAND COMPOSITION

Materials useful in making unitary strands of the present inventioninclude a wide variety of thermoplastic elastomers. An elastomer is asubstance which, in a stable form when stretched and released, willretract to resume its original dimensions, or nearly so. Some preferredelastomers are defined by ASTM Special Technical Bulletin No. 184,requiring that after the elastomer: is stretched at room temperature totwice its original length; is held for a five minute period; and, isreleased; it returns to within 10 percent of its original length withinfive minutes. Furthermore, it is a requirement of preferred elastomersfor use according to the present invention that they readily soften ormelt to an extrudable viscosity.

Suitable thermoplastic elastomers include elastomeric ethylene-propylenerubbers and random or block polymers of ethylene and two other monomerssuch as propylene or a diene, for example, 1,4-hexadiene. Preferably,the ethylene content is from about 50 to 70 weight percent, and morepreferably 55 to 65 percent by weight. Also, preferably, the propylenecontent is from 25 to 50 percent by weight, more preferably 35 to 45percent by weight. Preferred diene content is from about 0.5 to 4.0weight percent, more preferably 1 to 3 weight percent. For preferredelastomers according to the present invention preferred dienes include:dicyclopentadiene; 1,4-hexadiene; methylene norbornene; ethylidenenorbornene; cyclooctadiene; or structurally similar compounds.

Other suitable elastomeric polymers can be selected from severalchemical classes including: block copolymers of aromatic-aliphaticpolymers, particularly the linear ABA, radial A-(BA)_(n) and multiblockABABA polymers such as styrene-isoprene-styrene,styrene-butadiene-styrene, styrene-butylene-ethylene-styrene and thelike, ethylene-vinyl acetate copolymers with high vinyl acetate content(for example Elvax 260 which has a sufficient vinyl acetate content(28%) to exhibit elastomeric properties), and thermoplasticpolyurethanes and extrudable copolyester-ethers. Specific properties andsources of flexible polymers of these three classes are disclosed inKirk-Othmer, Encyclopedia of Chemical Technology, Vol. 8, pp. 626-640(3rd ed. John Riley & Son, N.Y., N.Y.), incorporated herein byreference.

Combinations, mixtures and blends of the thermoplastic elastomers canalso be used as alternatives to the pure elastomers.

Preferred thermoplastic elastomers are those generally referred to asABA block copolymers. Examples of these were listed above and includestyrene-isoprene-styrene, styrene-butadiene-styrene andstyrene-ethylene-butylene-styrene. A family of such block copolymers arecommercially available through Shell Chemical Company under the tradename "Kraton." Specific examples that are particularly useful forpreparing unitary strands of this invention are Kraton 1107, Kraton1111, Kraton 1101 and Kraton G 1657. Blends of these block copolymersmay also be useful in forming unitary strands according to theinvention.

Other components besides the thermoplastic elastomers may be utilized inunitary elastic strands. For example, many of the "Kraton" polymers canbe made available as blends with mineral oil. Aromatic block reinforcingresins may, in some instances, be used to increase the size of the endblock domains and increase the strength of the compositions. Lightstabilizers, antioxidants and pigments may also be added. Generally eachof the components of the compositions must be stable under extrusionconditions used to prepare the strands.

Typical conventional antioxidants usable include: thioethylenebis(3,5-di-tertiary-butyl-4-hydroxy)hydrocinnamate; tetrakis[methylene3-(3',5'-ditertiary-butyl-4'-hydroxyphenyl)propionate]methane;1,6-hexamethylene bis(3,5-ditertiary-butyl-4-hydroxy)hydrocinnamate;and, octadecyl(3,5-ditertiary-butyl-4-hydroxy)hydrocinnamate.

Typical conventional light stabilizers utilizable in compositionsaccording to the present invention include phenolics such as2-(2H-benzotriazol-2-yl)-p-cresol; octaphenyl salicylate;2-(2'-hydroxy-3',5'-tertiaryamylphenyl)benzotriazole; and,2,4-dihydroxybenzophenone.

Other components which may be utilized in compositions according to thepresent invention include pigments, antiblock agents, fragrances, slipagents, fillers and dyes. Typically, such materials may be incorporatedin amounts up to a total of about 20% of the weight of the strand,without substantially detrimentally affecting operation of the strand.In preferred applications of this invention, pigment is incorporated toimpart desired color and opacity to the strand. A typical preferredpigment is titanium dioxide.

EXAMPLE 1

A mixture of the following components was made, heated to about 200° C.,and was processed from a 30.0 millimeter (mm) extruder through aprofiled die such as illustrated in FIG. 4, with the followingdimensions: height of thicker regions (ribs) 0.38 mm; height of thinnerregions of 0.15 mm; width of thicker regions (ribs) 1.27 mm; width ofthinner regions (spacing between ribs) 1.65 mm. All percentages are byweight: 67.77% of a blend of 71% styrene-butadiene-styrene blockcopolymer and 29% plasticizing oil (Kraton 4141, Shell Chemical Co.,Oakbrook, Ill.), 13.49% ethylene-vinyl acetate copolymer (Elvax 260polymer, Dupont, Wilmington, Del.), 13.02% polyalpha-methylstyrene(Amoco 18-290, Amoco Chemical Corp., Chicago, Ill.), 0.48% Tinuvin Pultraviolet light stabilizer (Ciba-Geigy Corporation, Cranston, R.I.),0.48% Irganox 1010 antioxidant (Ciba-Geigy Corporation, Ardsley, N.Y.)and, 3.0% of a 50:50 mixture of polypropylene and titanium dioxide, CBE101 P (C. B. Edwards, New Hope, Minn.). The cross-section of theresulting elastic strand had the same shape and approximately the samedimensions as the die orifice. The extrusion conditions were: screwspeed 37 rpm, die pressure about 2300 psi (15850 kPa); and, line speedabout 10.67 meters per minute.

EXAMPLE 2

Using the method and die of Example 1, and a similar die plate, thefollowing copolymer was extruded to provide an elastic strand: anethylene-vinyl acetate copolymer which was 46% by weight vinyl acetate(Elvax 46, Dupont, Wilmington, Del.). The profile of the die plate hadthe following dimensions: rib height 0.5 mm; rib width 1.61 mm;transition region thickness 0.15 mm; transition region width 2.16 mm.The extrusion conditions were: screw speed 37 rpm; die pressure 816 psi;(5620 kPa); melt temperature 107° C.; and, line speed about 4 meters perminute. The cross-section of the resulting elastic strand had the sameshape and profile and approximately the same dimensions as the dieorifice.

EXAMPLE 3

Using the method of Example 1, and a die plate similar to that ofExample 1, the following formulation was extruded to provide an elasticstrand: 65.00% of a blend of 71% by weight styrene-butadiene-styreneblock copolymer and 29% plasticizing oil (Kraton 4141, Shell ChemicalCo., Oakbrook, Ill.), 13.00% ethylene-vinyl acetate copolymer (Elvax260, Dupont, Wilmington, Del.), 5% antiblock agent CBE 13782E (C. B.Edwards, New Hope, Minn.), 1% erucamide slip concentrate, Ampacet 10110(Ampacet Corp., Mt. Vernon, N.Y.), 12.50% Amoco 18-290, 2% CBE 101 P (a50:50 mixture of polypropylene and titanium dioxide), 0.75% Irganox 1010antioxidant and 0.75% Tinuvin P antioxidant. The profile of the dieplate had the following dimensions: rib height 0.229 mm; rib width 1.270mm; transition region thickness 0.18 mm; transition region width 1.6 mm.The extrusion conditions were: screw speed 41 rpm; die pressure 3850 ps;(26500kPa), melt temperature about 190° C.; and, line speed 10.67meters/min. The cross-section of the resulting elastic strand had thesame shape and profile, and approximately the same dimensions, as thedie orifice, except that the width of the transition regions had a lowercaliper than the orifice.

EXAMPLE 4

Using a sample of the elastic strand from Example 3, an unstretched and200% stretched sample were set on a sheet of 38 micrometer polyethylenefilm and were heat sealed thereto using a "Sentinel" brand sealer Model808 (Packaging Industries Group, Hyannis, Mass.). Attachment wasconstructed under pressure of about 290 kPa, a temperature of about 130°C. and a dwell time of five seconds. Each of the samples appeared sealedsecurely to the polyethylene film.

EXAMPLE 5

A 7.62 cm sample of the elastic strand of Example 3 was elongated 200%(to about 23 cm) and placed in a 65° C. oven for two minutes. The samplewas allowed to cool, and the tension was released. A 15 cm test area wasmarked and the elastic was placed at 65° C. for five minutes under notension. After cooling, the 15 cm test area had shrunk to about 8.4 cm(45%).

EXAMPLE 6

A mixture of the following components was made and processed byextruding through a slot extrusion die into a nip where one roller wasembossed with parallel grooves around the entire circumference,similarly to FIG. 11. The embossed pattern consisted of rectangulargrooves with a width of 1.14 mm and a depth of 0.2 mm. The grooves werespaced 1.5 mm apart.

The mixture consisted of: 65.50% of a blend of 71% by weightstyrene-butadiene-styrene block copolymer and 29% plasticizing oil(Kraton 4141, Shell Chemical Co., Oakbrook, Ill.), 13.00%ethylene-vinylacetate copolymer (Elvax 260, DuPont, Wilmington, Del.),12.50% poly-alpha-methyl-styrene (Amoco 18-290, Amoco Chemical Corp.,Chicago, Ill.), 5.00% antiblock agent (CBE 13782 E, C. B. Edwards, NewHope, Minn.), 1.00% UV stabilizer (Tinuvin P, Ciba-Geigy Corp.,Cranston, R.I.), 1.00% antioxidant (Irganox 1010, Ciba-Geigy Corp.,Ardsley, N.Y.), and 2.0% of a 50:50 mixture of titanium dioxide andpolypropylene (CBE 101 P, C. B. Edwards, New Hope, Minn.).

The extrusion conditions were screw speed: 31 rpm; melt temperatureabout 200° C.; and, line speed about 10 m/min. The cross-section of theresulting elastic film had the same shape and profile as the embossedchill roller.

EXAMPLE 7

Using the method and embossed chill roller of Example 6, a profiledelastic film was made from Santoprene 201-87 thermoplastic rubber(Monsanto Chemical Co., Akron, Ohio).

The extrusion conditions were: screw speed 42 rpm; melt temperature 220°C.; and, line speed about 5 m/min. The cross-section of the resultingelastic film had the same shape and profile as the embossed chillroller.

It is to be understood that while certain embodiments of the presentinvention have been illustrated and described, the invention is not tobe limited to the specific forms or arrangements herein described andshown.

What is claimed and desired to be secured by Letters Patent is as follows:
 1. An elastic strand construction composed of a stretchable elastomeric material and comprising(a) a plurality of laterally spaced longitudinal ribs, each of said ribs having an overall first thickness of from 0.1 mm to 0.635 mm and an overall width of between about 0.25 mm and about 5.1 mm; and overall width of between about 0.25 mm and abut 5.1 mm; and (b) a substantially continuous longitudinal transition zone extending between and attached to each of the longitudinal ribs, each transition zone having a second thickness less than said first thickness such that the ratio of said first thickness to said second thickness is from about 2/1 to 10/1 and each transition zone has an overall width of between about 0.25 mm and about 5.1 mm, the elastomeric material selected to provide the elastic strand with elasticity suitable to safely stretch around an arm, leg, or neck to provide a closing or sealing relationship.
 2. An elastic strand arrangement according to claim 1 wherein:(a) said elastomeric strand has opposite first and second faces; and (b) said second face is substantially flat and said ribs extend along said first face.
 3. An elastic strand arrangement according to claim 1 wherein:(a) each of said ribs has an overall width, the sum of which divided by the number of ribs is an average width of said ribs; and (b) each transition zone width is at least 50% said average width of said ribs.
 4. An elastic strand arrangement according to claim 1 wherein said longitudinal ribs extend substantially parallel to one another.
 5. An elastic strand construction composed of a stretchable elastomeric material and comprising:(a) an elastomeric strand having opposite first and second faces; (b) said second face is substantially flat to facilitate mounting to a substrate, and has ribs extending along said first face; (c) said ribs comprising a plurality of laterally spaced longitudinal ribs, each of said ribs having an overall first thickness of from 0.1 mm to 0.635 mm; and (d) a substantially continuous longitudinal transition zone extending between and attached to each of the longitudinal ribs, each transition zone having an overall second thickness less than said first thickness such that the ratio of said overall first thickness to said overall second thickness is from about 2/1 to 10/1, the elastomeric material selected to provide the elastic strand with elasticity suitable to safely stretch around an arm, leg, or neck to provide a closing or sealing relationship.
 6. An elastic strand arrangement according to claim 5 wherein:(a) each of said ribs has an overall width, the sum of which divided by the number of ribs is an average width of said ribs; and (b) each transition zone has an overall width of at least 50% said average width of said ribs.
 7. An elastic strand arrangement according to claim 5 wherein said longitudinal ribs extend substantially parallel to one another.
 8. An elastic strand arrangement according to claim 5 wherein each rib has an overall thickness of between about 0.5 mm and 0.635 mm.
 9. An elastic strand arrangement according to claim 5 wherein:(a) each rib has an overall width of between about 0.25 mm and about 5.1 mm; (b) each transition zone has an overall width of between about 0.25 mm and about 5.1 mm. 